Fat can apply to multiple hides for small and medium ones, anyway starting the leather making process isn't that difficult, if you found enough copper nuggets for a hammer and pick then you should be able to mine under the nuggets for enough for an anvil (9 ingots) and saw and chisel 2 combined.
With 3 boards you can make a barrel and with 5 "hard" stone blocks that have been leavened (break the 8 blocks touching it) you can make a quern to grind lime bearing stones (or buy lime directly from a trader) this all now requires an anvil for saw and chisel. but finally with a ratio of 1 lot of lime with 1 liter of water up to 50 in the barrel you can soak the hides and they no longer rot.